1. Field of the Invention
This invention relates to an optical-electronic array module for connecting to a fiber optic cable and to electronic devices on an electronic circuit board, and more particularly to an arrangement of the module that facilitates assembly of the module and alignment and connection of the module to the fiber optic cable electronic circuit board.
2. Related Art
Optical-electronic transmitters and receivers on an optical-electronics module are conventionally coupled to optical signals via a fiber-optic cable. The optical fibers of the cable are typically aligned to optics of the optical-electronic transmitters and receivers with a required precision of about 5 microns.
It is also conventional practice that the optical-electronics module with the transmitters and receivers are supplied to a customer having electrical circuit on the customer""s circuit board to be connected to the optical-electronic transmitters and receivers. Generally the plane of the optical paths in the optical coupler is parallel to the plane of the customer""s electronic circuitry, and the plane of the electronic inputs and outputs (xe2x80x9cI/Oxe2x80x9d) of the optical receivers and transmitters is orthogonal to the plane of the I/O of the customers electronic circuitry. Therefore, in order to connect the I/O of the electronic circuitry on the customer""s board to the electrical I/O of the optical-electronic transmitters and receivers it is necessary to turn the electrical path between the respective sets of I/O.
Referring to FIG. 1, the alignment of optical paths and the turning of the electrical path between I/O sets is illustrated in a prior art module 100, which includes a carrier 110 mounted on a heat sink 180, an optical-electronic die 120 mounted on the carrier 110, a coupler 140, a signal conditioning die 190, a flexible cable 130, a first circuit board 170, and C4 solder balls 175. The circuit board 170 has die 190 mounted thereon. The die 190 has signal conditioning circuitry that interconnects to and operates with the optical-electronic circuitry of the die 120 by means of the flexible cable 130. The die 190 also interconnects to a customer""s circuit board, second circuit board 172, via conductors (not shown) and C4 solder balls 175.
The carrier 110 is for structural purposes and for conducting thermal energy away from the die 120. The carrier 110 does not have embedded conductors, but the carrier 110 itself is conductive, and it electrically connects a cathode on the laser die 120 to ground. The prior art apparatus uses two carriers, side-by-side. Only one of the carriers 110 is shown in FIG. 1. On one of the carriers 110, the die 120 is a laser die. On the other carrier 110, the die 120 is a photo detector die. (The term xe2x80x9coptical-electronic diexe2x80x9d will be used herein to refer to either a laser die or a photo detector die.) In FIG. 1, the die 120 is bonded to the carrier 110, such as with a die attach epoxy, on the same side of the carrier 110 as an optical coupler 140. The carrier 110 has alignment holes for receiving pins 142 from the coupler 140. The coupler 140 attaches to the carrier 110 with a retainer (not shown) and alignment pins 142.
A fiber-optic cable 160 having a number of embedded fibers 162 mates to the optical coupler 140. A connector 150 of the fiber-optic cable 160 has alignment holes for receiving alignment pins 152 from the coupler 140. The coupler 140 attaches to the connector 150 with a retainer (not shown) and alignment pins 152.
The flexible cable 130 is a composition of gold-coated, copper conductors etched in a polyimid and covered with an insulating jacket. The flexible cable 130 is attached at attachment 137 to the first circuit board 170 at one end and at attachment 134 to carrier 110 for the optical-electronic die 120 at the other end. The flex cable 130 is electrically connected at 132 to the die 120 by wire bonds 136. Likewise, the flex cable 130 is electrically connected at 139 to die 190 with wire bonds 138.
The flex cable 130 provides a 90 degree turn between the I/O plane of the optical-electronic die 120 and the customer""s board, second circuit board 172, however, it is problematic to use the flex cable to provide this 90 degree bend because of its cost and because of the relatively large number of interconnections at 132, 134, 137, etc. Also, with conventional arrangements such as that of FIG. 1 it is problematic to achieve required alignment precision since it requires expensive and time consuming xe2x80x9cactivexe2x80x9d alignment, according to which the optical-electronic die is powered and its output monitored, then secured with adhesive once alignment is optimized. There is therefore a need for an improved optical-electronics module.
The foregoing need is addressed in an optical-electronic module having a submount. The submount forms an aperture which extends all the way through the submount. An optical-electronic die is mounted on a first side of the submount. The module also has an optical coupler, with a fiber-optic path in the coupler, for coupling optical signals from or to a fiber-optic cable on a first end of the coupler and for coupling the optical signals from or to the die at a second end of the coupler. The second end of the coupler has a feature matching the submount aperture and inserted into the submount aperture. An optical input or output of the die faces the second end of the coupler and is aligned to the coupler fiber-optic path and optically coupled to the fiber-optic path through the aperture.
In another aspect, pads for electronic inputs or outputs on the optical-electronic die face, align with, and are electrically coupled to first electrical pads on the submount first side.
In another aspect, the aperture is tapered, narrowing toward the submount first side, and the coupler feature matching the submount aperture comprises a tapered nose narrowing toward the coupler second end.
In another aspect, the coupler end proximate to the die (the coupler second end) is sub-flush to the submount first side. From the coupler side which is proximate the die, the coupler extends through the submount aperture and beyond the submount second side.
In still another aspect, the submount first side is in a first plane, and the submount has a third side in a plane oblique or perpendicular to the first plane. The third side has second electrical pads, for connecting to electrical pads on a circuit board. The second electrical pads are connected by conductors of the submount to respective ones of the first electrical pads, so that electrical paths from the electronic inputs or outputs of the optical-electronic die turn by at least an acute angle from the first to the second submount electrical pads.
In a still further aspect, the coupler has mechanical pads for coupling to the circuit board. In an alternative, the coupler mechanical pads are on a bottom side of the coupler and the coupler bottom side is in the same plane as the submount third side.
In a method form of the invention, a method for fabricating an optical-electronic array module includes a providing a submount having first and second opposing sides and a third side essentially perpendicular to the first submount side. The first and third submount sides have an adjoining edge, and the submount forms an aperture extending through the submount from the first to the second sides. Conductive traces are formed on the first and third sides and adjoining edge of the submount using a shadow mask. The traces interconnect electrically conductive pads on the first submount side and second electrically conductive pads on the submount third side. An optical coupler is inserted into the submount aperture and secured therein. The coupler has a fiber-optic path therein for coupling optical signals from or to a fiber-optic cable on a first end of the coupler and for coupling, at a second end of the coupler, the optical signals from or to a die mounted on the submount first side. The second end of the coupler has a feature matching the submount aperture. An optical input or output of the die is aligned to the coupler fiber-optic path facing the second side of the coupler concurrently with aligning pads on the die for electrical inputs or outputs to the electrical pads on the submount first side.
In a further aspect, the method includes mounting the die on the submount, wherein the optical inputs or outputs of the die are aligned to the coupler fiber-optic path, and the electronic input or output pads on the die are aligned to first electrical pads on the submount first side prior to the die being mounted on the submount.
In a still further aspect, the optical inputs or outputs of the die are aligned to the coupler fiber-optic path, and the electronic input or output pads on the die are aligned to first electrical pads on the submount first side after the coupler is secured to the submount.
In yet another aspect, the optical inputs or outputs of the die are aligned to the coupler fiber-optic path, and the electronic input or output pads on the die are aligned to first electrical pads on the submount first side with the die deenergized.
It is an object of the invention to bend an electrical path between I/O of a circuit board and I/O of an optical-electronic die without using a flexible cable, thus reducing cost, shortening the electrical path, and improving electrical properties of the interconnections.
It is another object of the invention to facilitate precise alignment between fiber-optic paths and optics of devices on the optical-electronic die.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings.